This invention relates to improvements in forced air heating systems for homes and other types of buildings wherein the fireplace is utilized as a heat source for the forced air system. More particularly the invention is directed to such a system which includes a conventional forced air furnace operating in concert with a fireplace.
Forced air heating systems which utilize a combination of a fireplace and forced air furnace have been devised in the past, such as those shown in Slayter et al. U.S. Pat. No. 2,186,539 and Glover U.S. Pat. No. 3,834,619. However such systems do not capitalize fully on the energy-saving potential of which such systems should be capable because of several basic drawbacks in design. For example, the heating elements of the furnace portion of such prior systems are typically treated as the primary rather than secondary heat source, as evidenced by the fact that they are operated in response to the room thermostat in the conventional manner even though the fireplace may also be operating and producing substantial heat. This type of arrangement, which treats the fireplace merely as an auxiliary or secondary heat source even though in full operation, results in much more use of the furnace heating elements, and therefore much more use of electrical or other fuel energy, than is desirable in a system of this type whose objective should be to minimize the usage of such electrical power or other fuel energy.
Furthermore, such systems require that at least a portion of the heating air must always pass through the fireplace heat exchanger even though the fireplace may be totally inoperative. If the fireplace is located a substantially great distance from the furnace, which is often the case, this results in an unnecessarily lengthy duct path between the furnace and the individual room outlet registers in a system such as Slayter's where the fireplace is located on the exhaust side of the furnace. The long duct path in turn causes wasteful energy loss from the furnace-heated air when the fireplace is inoperative. Alternatively, in a system such as Glover's where the fireplace is located in the furnace inlet or cold air return duct, the heat generated by the fireplace when operative will be unnecessarily wasted by being required to travel to the furnace if the distance from the fireplace to the furnace is very lengthy, as may often be the case.
Accordingly what is needed is a system which is designed to utilize the fireplace as the primary heat source when operative and thereby require less utilization of the conventional heating elements than has previously been the case, and which does not require passage of the circulating heating air medium from the furnace through the fireplace heating chamber when the fireplace is inoperative, nor from the fireplace heating chamber through the furnace when the fireplace is operative.